1. Field of the Invention
This invention relates to a lenticular lens sheet used for televisions of rear projection type, a manufacturing method of the lenticular lens sheet and a transmission screen.
2. Description of the related art
There are two types of lenticular lens sheets. One type is a two-side lenticular lens sheet, and the other type is a one-side lenticular lens sheet.
The two-side lenticular lens sheet comprises: an incident side lenticular lens provided on the incident side into which the light comes, for diffusing the light in the horizontal direction; and an output side lenticular lens provided on the output side out of which the light is emitted, for calibrating the optical axis. The light absorbing layers (black stripes) are formed on the surface of the output side, at non-output portions (non-transmissive portions) for the light condensed by the incident side lenticular lenses, for enhancing the contrast. In the case of using the two-side lenticular lens sheet, diffusion of the light in the vertical direction is controlled by mixing a diffusing material into the sheet, or by providing lenticular lenses of vertical diffusion type on the incident side of the Fresnel lens arranged on the incident side (light source side) with respect to the two-side lenticular sheet.
On the other hand, contrast of the one-side lenticular lens sheet is enhanced by coloring the sheet.
However, the two-side lenticular lens sheet has a difficulty in achieving a fine lens pitch for the following reasons.
First, the thickness of the sheet becomes thinner if the lens pitch is made smaller, because the output portion has to be provided near the focuses of the incident side lenticular lenses in order to increase the area of the light absorbing layer.
Second, it is difficult to position the incident side lenticular lenses and the output side lenticular lenses to coincide with each other.
Third, the reproduction of the lens shape is not good with the extrusion method.
Furthermore, the two-side lenticular lens sheet tends to be damaged while it is transported or used, because its output side has a minute shape.
On the other hand, it is difficult to sufficiently enhance the contrast of the one-side lenticular lens sheet, even if the sheet is colored.